In many applications, such as disinfection, odour generation and air humidification, liquids or fluids are needed to be dispensed into micro-droplets or aerosols through atomization or vaporization. Normally, for medical purpose, such devices may contain a heating unit or an air compressing pump. However, these devices are generally limited by the decomposition of the medicinal products due to the high temperature, or by the risk of introducing external contamination because of the direct contact of air with medicine, or by the concomitant noise.
To satisfy the special demands of delivering medicines by respiratory pathway, the piezoceramic based atomization technology, i.e., by vibrating a micro-perforated membrane attached to a piezoceramic, is developed by manufacturers these years. Briefly, according to this technique, the micro-perforated membrane contact with a liquid is vibrated at an ultrasonic frequency by an activated piezoceramic, and then the liquid is drawn onto the top surface of the membrane, thus forming a film thereon. The liquid film absorbs vibrational energy from the membrane with vibrating direction perpendicular to the surface, and forms standing waves. As the amplitude of the given vibrational frequency is increased, the waves become unstable, and finally collapse at some critical point. As a result, micro-droplets of liquid are ejected from the films directed normally to the membrane.
However, most of the commercially available piezoceramic based atomization devices are designed for water-based or low viscosity liquids. Actually, many medicinal liquids possess relatively high viscosity, ranging from several tens to more than 300 centipoises (cP), and may not be water-based. Unfortunately, these high viscosity liquids cannot be atomized by aforementioned devices, owing to the fact that the viscous liquid film on the surface of the membrane clogs the micro holes and thus blocking the atomization. Therefore, it would be desirable to develop an effective method that capable of forming micro-droplets from high viscosity liquids by piezoceramic based atomization.